QT 5 connect（）函数连接textEditor和MainWindow [英] QT 5 connect() function to connect the textEditor and the MainWindow

问题描述

我正在学习Qt 5的一些示例代码从web，但我不能编译它。我有几个文件：
在mainwindow.h，我有我的代码：

I am learning Qt 5 with some example code from web, but I cannot compile it. I have several files as: in mainwindow.h, I have my code:

class MainWindow : public QMainWindow {
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
private:
    QTextEdit *textEdit;
};

类的实现在mainwindow.cpp中，如

The implementation of the class is in mainwindow.cpp, as

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) {
    setWindowTitle("TextPad [*]");
    textEdit = new QTextEdit(this);
    setCentralWidget(textEdit);
    connect(textEdit,&QTextEdit::textChanged,this,this->setWindowModified(true));
}

在我的main.cpp中，它很简单，因为

And in my main.cpp, it is quite simple, as

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MainWindow window;
    window.show();
    return app.exec();
}

我想要做的是在窗口标题中有一个* ，如果我改变了textEditor中的文本，所以我使用一个connect（）函数。问题我无法正确编译，错误消息是

What I want to do is the have a "*" in the window title, if I have changed the text in the textEditor, so I use a connect() function. The problem I cannot compile it correctly, the error message is as

error: invalid use of void expression
     connect(textEdit,&QTextEdit::textChanged,this,this->setWindowModified(true));

任何帮助都非常感谢！

推荐答案

更改

connect(textEdit,&QTextEdit::textChanged,this,this->setWindowModified(true));

到

connect(textEdit,SIGNAL(textChanged()),this,SLOT(myTextChanged()));
//or you can use alternate form
connect(textEdit,&QTextEdit::textChanged,this,myTextChanged);

并定义槽位

void MainWindow::myTextChanged() {
    setWindowModified(true);
}

connect只需要信号/槽的名称（使用字 SIGNAL 和 SLOT ）或指向它的指针，使用函数指针样式，因此您不能将代码放置在 connect（）调用中执行。而是定义一个额外的插槽来实现所需的行为，如下所示。

connect() requires only either the name of the signal/slot (using the words SIGNAL and SLOT) or a pointer to it, using the function pointer style, so you cannot place code to execute in a connect() call. Instead define an extra slot to implement the desired behavior, as shown.

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